Did you know that a dowser, walking along divining for water, is actually sensing changes in the earth’s magnetic field? If you were able to shrink right down to miniature size and move across the surface of a common bipolar magnet, there would be no change in the magnetic field and it’s said to be uniform or “homogeneous”. Whereas, if you were able to walk across a Quadrapolar magnet, there would be large changes and the magnetic field is said to be non-uniform or “inhomogeneous” and produce magnetic field gradients.

Research indicates that humans are sensitive to small changes in magnetic field gradients, but not to the overall magnetic field (Rocard, 1964). Evidence supporting this has come from studies of the dowser reflex. A dowser, a person holding firmly onto a divining rod (see Fig. 1.12) will, under certain physical conditions, experience a force which results in an involuntary upward or downward movement of their rod. To skeptics the movement appears illusory, to believers it appears magical, but the effect has been consistently reported over the past 70 years by a number of authors. In the most-often performed experiment, a group of dowsers was made to walk along the same stretch of street. At points within 1 or 2 m of each other, they all had their divining rods pulled down to the earth.

Magnetic field measurements have shown that the dowser reflex occurs when the dowser passes through a region where the Earth’s magnetic field is not entirely uniform. This field anomaly produces a magnetic field gradient, which must exceed 0.1 mOe m_1 (8 mA m_2) to be detected. The speed with which the dowser passes through this field gradient also influences their magnetic reception. The dowser must pass through a 0.1 mOe m_1 field gradient within at least 1 s in order to detect it. Furthermore, the detection level can be increased by adding up the small differences in field gradients. Higher magnetic field gradients, however, lead to saturation and can only be detected by moving faster. Of additional interest is Rocard’s notion that although most people are sensitive, a good dowser has a more accurate and rapid reflex than the bad dowser.